北大别片麻岩中锆石U-Pb年龄离子探针初步测定  

Preliminary U-Pb ion probe age determination of zircons from gneisses, Northern Dabie Terrain

作　　者：陈道公[1] Etienne Deloule 夏群科[1] 程昊[1] 

机构地区：[1]中国科学技术大学地球和空间科学系,合肥230026 [2]法国CNRS,岩石地球化学研究中心南锡54501

出　　处：《岩石学报》2000年第2期199-202,共4页Acta Petrologica Sinica

基　　金：国家自然科学基金!(497940 42;49973 0 19);中国科学院(KZ51-AI-401-05)项目

摘　　要：对北大别鹿吐石和道士冲二个片麻岩中锆石进行了离子探针 U- Pb年龄测定。二个样品 13个颗粒的 2 0个有效测定点的年龄表明 ,鹿吐石片麻岩主要分布在 2 33～ 394Ma,道士冲片麻岩在 30 7～ 718Ma之间。道士冲片麻岩年龄的一致性程度要高于鹿吐石 ,两个样品均无低于 2 2 0 Ma的年龄信息。由于存在年龄的不一致性 ,这些年龄可能代表了由古老岩浆锆石和三叠纪的超高压变质锆石或者早白垩纪岩浆锆石所代表的混合、增生锆石。 Harker等所认为是典型北大别片麻岩中锆石 ,实际上也是在前寒武纪形成的岩浆锆石基础上叠加白垩纪形成的变质锆石的一种复杂锆石。因此 ,根据锆石年龄分布来看 ,它并不代表这些片麻岩就是在白垩纪时形成的 ,北大别很可能存在二种不同时代的片麻岩。Two zircon ages were determined for U-Pb ion probe analyses from Lutushi(LTS) and Daoshicong(DSC) gneisses, Northern Dabie Terrain(NDT). Twenty U-Pb ages from thirteen zircon grains indicated that the ages for LTS gneiss are mainly ranged between 233~394Ma and DSC gneiss between 307~718Ma. The degree of concordance for DSC gneiss is better than that of LTS gneiss. Both gneisses show no age information below 220Ma. Since there were exits of discordances, these zircon ages probably represented mixing and overgrowth of ancient magmatic zircons with Triassic ultra-high pressure metamorphic and Cretaceous magmatic zircons. Those which were treated by Harker et al. as typical gneisses occurred in NDT may also be complex zircons which are formed in Precambrian magmatic zircons with late Cretaceous metamorphic zircons. Therefore, according to their U-Pb ages and distribution of zircons, one cannot conclude that all the gneisses from NDT were formed at Cretaceous. There may be two different age gneisses in NDT.

关 键 词：片麻岩 锆石 铀-铅年龄 离子探针 

分 类 号：P588.345[天文地球—岩石学] P597[天文地球—地质学]